Title: oxford / 127 proof_toolkit

Front: PL-proof of weakening the consequent

Front: PL-proof of Contraposition 1

Front: PL-proof of Contraposition 2

Front: PL-proof of ex falso quodlibet

Front: [place holder]
when you have time, add all (or most) proofs in the MPL-toolkit (examples in LfP pp 206 to 218)